There is a technique for switching winding specifications of an electric motor by switching connection states of windings of the electric motor. Patent Literature 1 discloses a method for driving an electric motor by switching winding specifications using lead wires drawn out by separating the neutral points of windings, and by cooperatively operating the master-side inverter circuit and the slave-side inverter circuit when a winding specification is an open winding specification, or by operating the master-side inverter circuit when a winding specification is a star connection specification.